Abstract
Experiments have been carried out to determine whether intracellular transport of pancreatic secretory proteins is obligatorily coupled to protein synthesis or whether it is a separable process which can be independently regulated. To this intent, guinea pig pancreatic slices were pulse labeled with leucine-3H for 3 min and incubated post-pulse for 37 min in chase medium containing cycloheximide up to concentrations sufficient to inhibit protein synthesis by 98%. In controls, newly synthesized secretory proteins are transported over this interval to condensing vacuoles of the Golgi complex. Since the latter are recovered in the zymogen granule fraction upon cell fractionation, intracellular transport was assayed by measuring the amount of protein radioactivity found in the zymogen granule fraction after a (3 + 37) min incubation. The results indicated that at maximum inhibition of protein synthesis (5 x 10-4 M cycloheximide), transport proceeded with an efficiency ∼80% of control. Parallel radioautographic studies on intact slices confirmed these data and further indicated that all the steps of intracellular transport, including discharge to the acinar lumen, were independent of protein synthesis. We conclude that: (1) transport and protein synthesis are separable processes; (2) intracellular transport is not the result of a continuous delivery of secretory proteins from attached polysomes to the cisternae of the rough endoplasmic reticulum; and (3) transport is not dependent on the synthesis of "specific" nonsecretory proteins within the time limits tested.
Full Text
The Full Text of this article is available as a PDF (840.5 KB).
Selected References
These references are in PubMed. This may not be the complete list of references from this article.
- ENNIS H. L., LUBIN M. CYCLOHEXIMIDE: ASPECTS OF INHIBITION OF PROTEIN SYNTHESIS IN MAMMALIAN CELLS. Science. 1964 Dec 11;146(3650):1474–1476. doi: 10.1126/science.146.3650.1474. [DOI] [PubMed] [Google Scholar]
- Jamieson J. D., Palade G. E. Intracellular transport of secretory proteins in the pancreatic exocrine cell. I. Role of the peripheral elements of the Golgi complex. J Cell Biol. 1967 Aug;34(2):577–596. doi: 10.1083/jcb.34.2.577. [DOI] [PMC free article] [PubMed] [Google Scholar]
- Jamieson J. D., Palade G. E. Intracellular transport of secretory proteins in the pancreatic exocrine cell. II. Transport to condensing vacuoles and zymogen granules. J Cell Biol. 1967 Aug;34(2):597–615. doi: 10.1083/jcb.34.2.597. [DOI] [PMC free article] [PubMed] [Google Scholar]
- Morimoto T., Tashiro Y., Matsuura S. Chase of newly synthesized proteins in guinea-pig pancreas with cycloheximide. Biochim Biophys Acta. 1967 May 30;138(3):631–633. doi: 10.1016/0005-2787(67)90567-9. [DOI] [PubMed] [Google Scholar]
- NATHANS D. PUROMYCIN INHIBITION OF PROTEIN SYNTHESIS: INCORPORATION OF PUROMYCIN INTO PEPTIDE CHAINS. Proc Natl Acad Sci U S A. 1964 Apr;51:585–592. doi: 10.1073/pnas.51.4.585. [DOI] [PMC free article] [PubMed] [Google Scholar]
- PALADE G. E., SIEKEVITZ P. Pancreatic microsomes; an integrated morphological and biochemical study. J Biophys Biochem Cytol. 1956 Nov 25;2(6):671–690. doi: 10.1083/jcb.2.6.671. [DOI] [PMC free article] [PubMed] [Google Scholar]
- SIEKEVITZ P., PALADE G. E. A cytochemical study on the pancreas of the guinea pig. 5. In vivo incorporation of leucine-1-C14 into the chymotrypsinogen of various cell fractions. J Biophys Biochem Cytol. 1960 Jul;7:619–630. doi: 10.1083/jcb.7.4.619. [DOI] [PMC free article] [PubMed] [Google Scholar]